The collective bargaining agreement between the NFL and its officials expires the last day of May, and negotiations haven't made much progress, according to sources.

FoxSports.com obtained a letter the NFL sent to its officiating-scouting department, in which the league asked for help in identifying possible candidates if it needs to hire replacements.

"Negotiations are ongoing, and should the two sides reach an agreement in the near future, there will be no need to hire additional officials," Ron Baynes, the NFL's director of recruiting officials, wrote in the letter, according to FoxSports.com. "This is a contingency plan to make sure the NFL season will continue on schedule as planned."

If a new deal is not struck, the NFL would consider locking out officials and hiring college and semi-pro officials, sources confirmed.

Those hires would not come from the BCS conferences because the officials in those games are run by NFL officials, and the league doesn't want to put the BCS officials in an awkward situation.

The NFL could turn to a few elite NCAA officials who have retired. The next negotiating session is scheduled for May 16. Jeff Pash is the NFL's lead negotiator.

Another negotiating session is expected later this month, NFL Referees Association executive director Tim Millis said Thursday. Millis said he is "surprised by the timing" of the league memo.

Millis said the NFL "did something like this" during contract talks in 2001, but did not do it during negotiations in 2006.

"There's not any one hang-up," Millis said of the sides' talks. "It's all part of the process. We have not talked to anyone about this (letter). It's not a product of any CBA negotiations.

NFL spokesman Greg Aiello said Thursday: "We expect to reach an agreement, but must have contingency plans in place."